Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant. Balls having a solid construction generally provide a very durable ball while also providing maximum distance. Solid balls are generally made with a solid core (of one or more layers) encased by a cover of at least one layer. Typically, solid cores are made of polybutadiene that are chemically cross-linked with zinc diacrylate (or similar cross-linking agents). The covers are generally a material such as SURLYN®, an ionomer resin produced by DuPont, or, more recently, polyurethane. Such a combination imparts a high initial velocity to the ball that results in improved distance. Because these materials can be very rigid, many two-piece balls have a hard “feel” when struck with a club. Likewise, due to their hardness, these balls can also have a relatively low spin rate, which provides greater distance.
Wound balls typically have either a solid rubber or liquid center core around which many yards of a tensioned elastomeric material are wound and are covered with a durable cover material such as ionomer or polyurethane. Wound balls are generally softer and provide more spin than do solid golf balls. This enables a skilled golfer to have better control over ball flight. Particularly, with approach shots into the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.
The design and technology of golf balls has advanced to the point that the United States Golf Association has instituted a rule prohibiting the use of any golf ball, in a USGA sanctioned event, that can achieve an initial velocity of greater than 255 ft/s when struck by an implement having a velocity of 143 ft/s (referred to hereinafter as “the USGA test”).
Manufacturers place a great deal of emphasis on producing golf balls that consistently achieve the highest possible velocity in the USGA test without exceeding the limit, which are available with a range of different properties and characteristics, such as velocity, spin, and compression. Thus, a variety of different balls are available to meet the needs and desires of a wide range of golfers.
Regardless of the construction of the ball, players generally seek a golf ball that delivers maximum distance, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with high initial velocities.
As a result, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers at all skill levels, and seek to discover compositions that provide the performance of a high compression ball with lower compression.
The physical characteristics of a golf ball are determined by the combined properties of the core, any intermediate layers, and the cover. These, in turn, are determined by the chemical compositions of each. The composition of some balls will provide for increased distance. Other compositions provide for improved spin. Manufacturers are constantly looking to develop the ideal materials. Thermoplastic polyurethane ureas for example, have been examined for their innate ability to provide material having very high tensile strengths, which is a very desired property in the make-up of a golf ball.
Polycarbonate-urethane elastomers (PCUE) are thermoplastic in nature. That is, they can be processed by methods that involve melting or dissolving the polymer to “re-shape it.” The molecular structure of PCUEs generally consists of alternating high-melting “hard” urethane segments and liquid-like “soft” segments. Hard segments are almost always the reaction product of an aromatic or aliphatic diisocyanate and a low molecular weight, chain-extending dialcohol or diol. Soft segments are usually synthesized from (polyether or polycarbonate) polyols with terminal hydroxyl (—OH) groups. The hydroxyl creates a urethane group, while the reaction between isocyanates and existing urethane groups will form allophanate groups that can produce minor amounts of covalent cross-linking. When a PCUE is heated, the hydrogen-bonded hard segments and any allophanate cross-links, both of which hold the polymer together at its use temperature, dissociate to allow the polymer to melt and flow. Dissolution in a polar solvent can also disrupt the hydrogen bonds that hold together the hard segments on adjacent chains. Once these virtual cross-links are broken, the polymer can be fabricated into golf balls. Upon cooling or solvent evaporation, the hard segments de-mix from the soft segments to re-associate by hydrogen bonding. This restores the original mechanical properties of the PCUE.
While conventional polyether and polycarbonate TPUs have high elongation and tensile strength, they also exhibit fairly high moduli. Therefore, there exists a need for a golf ball comprising a thermoplastic polycarbonate elastomer having improved golf ball performance. Therefore, by varying the hard segment of a PCUE during synthesis, a whole family of polymers of related chemistry can be produced having a wide range of hardness, modulus, tensile-strength properties and elongation.